1. Field of the Invention
The present communications system relates in general to multimedia (audio, video, and/or data) conferencing techniques, and in particular to a multimedia bridging system which utilizes an improved multipoint control unit and improved endpoint devices to provide a variety of features in a manner that constitutes a considerable improvement over the current art.
2. Description of the Prior Art
In the field of multimedia communications, a "bridge" or "multipoint consol unit" (MCU) is a computer-controlled device which includes a multiplicity of communication ports which may be selectively interconnected in a variety of ways to provide communication among a group of endpoint devices. MCUs are often used to establish multi-party conference calls. The state-of-the-art MCU is described in ITU Document H.243, "Procedures for Establishing Communication Between Three or More Audiovisual Terminals Using Digital Channels up to 2 Mbps," March 1993, and in ITU Document H.231, "Multipoint Control Units for Audiovisual Systems Using Digital Channels up to 2 Mbps," March 1993.
Generally speaking, such systems require conferences to be prearranged in advance. A series of steps must be performed in order to provide the system topology necessary to implement a multimedia conference call. Typically, the user calls a reservation agent who then directs the MCU to either prepare itself to receive calls at a given time, or to dial out to the user at a given time. These setup procedures are inconvenient, tedious, and inflexible. A clear need exists to provide for "spontaneous" or "on-demand" conferencing where the user does not need to invoke a reservation system to set up a multimedia conference.
Bellcore Generic Requirements GR-1337-CORE, Issue 1, September 1993 contains a description of a "spontaneous" conferencing system based on user control from a touch-tone (DTMF) keypad, i.e., with strings of numbers and letters, and audio feedback from stored announcements. This method is widely used in the audio bridging industry for voice calls, and in the Bellcore GR-1337-CORE proposal, the same method is applied to multimedia calls (voice/video).
The method of spontaneous conferencing widely used for audio-only calls, and applied to multimedia calls in GR-1337-CORE, suffers from the following difficulties that represent areas of possible improvement:
1. The strings of numbers require a long period of time to enter. 2. The codes required to perform operations are numerous and difficult to remember. 3. Feedback is limited to audio messages, and the length of these messages is frequently such that the process of conference setup is very slow. 4. The user must make an initial decision to contact the MCU for the purpose of establishing a conference. 5. The MCU contacted via the method of GR-1337-CORE may have no available resources with which to implement a multimedia conference. 6. The user is highly aware of the "seams" (i.e., procedural discontinuities) in the process of constructing the conference. 7. The person initiating the addition of a new party to the conference may wish to have a private conversation with the new party prior to allowing this party into the conference. The purpose of this conference might be to confirm the identity of this new party while allowing the conference to continue. However, existing systems are not equipped to provide such a private conferencing mode. 8. The person initiating the conference might wish to select the conference mode of operation which, for example, determines the selection criteria to be applied in determining the party or parties which will be broadcast to other conference participants at any given moment in time. Typical conference modes include chair mode voice-activated mode, and various other modes known to those skilled in the art. It would be desirable to change this mode during the conference upon command, although such changes are difficult or impossible to implement with state-of-the-art systems.
U.S. Pat. No. 4,653,090, which is owned by the current applicant, describes a system of graphics-based call management which establishes a voice and/or data conference using a graphical user interface. U.S. Pat. No. 4,953,159 (also owned by the current applicant) describes an audio graphics conferencing arrangement controlled by a graphics user interface. In both of the aforementioned patents, graphics-based call management is limited to voice and data calls, and is not applied to video calls.
U.S. Pat. Nos. 5,014,267, 4,686,698, 4,847,829 and 4,710,917 describe a system of video conferencing terminals and a specialized network to support them. Such systems may provide some level of control over multi-media conference, but have the deficiency of requiring a special-purpose video network that may not be generally useful, and may be limited in physical size. Also, such systems only provide enhanced multi-media conferencing features to endpoints that are directly connected to the special-purpose network. In this context, such special-purpose networks can be regarded as one instantiation of the video equivalent of the audio PBX, or private branch exchange, providing special features to physically attached endpoint devices.